Leg prostheses can provide an artificial ankle, and artificial knee, or both an artificial ankle and an artificial knee. A transfemoral prosthesis is a prosthesis designed for above the knee amputees. Transfemoral prostheses are generally more complicated than transtibial prostheses, as they must include a knee joint.
Nearly all current commercial transfemoral comprising prostheses are energetically passive devices. That is, the joints of the prostheses either store or dissipate energy, but do not provide net power over a gait cycle. The inability to deliver joint power impairs the ability of these prostheses to restore many locomotive functions, including walking up stairs and up slopes. Moreover, there is a need for a leg prosthesis that provides a more natural gait behavior.